Damaged screen - not all segments light on

When the screen does not allow all segments to be seen, it may be one of several faults:

- Bad connections of the lower zebras. The solution is to clean with contact cleaner the contacts in both circuit, keyboard and zebras; and if it continues to not working, then change the zebras. 

- Bad connections of the lightly soldered screen pins. First you need to check with a flat screwdriver, pussing lightly to a side all pins, one by one. If any gives, then you will have to resolder it. A small solder will suffice. Normally there is no need to add more solder - the one already applied is enough. Make sure that contact is made by applying downward pressure to the pin with the flat screwdriver that you used to test it.

- Bad connection between the LCD and the screen driver. If the two previous steps have failed, you need to check this one to discard the last one. You need to:

• unsolder the screen, by prying softly with a plier while heating in the solder pad on the keybard. Do not keep the heat for long or the driver will be damaged!
• Takin upmost care of not touching the screen connection pins, carefully pry out the upper and lower black metal clips that hold together the screen and screen drivers. Be very careful with the screen pins - it is very easy to bend them or separate from the body!!
• separate the two halves (screen and screen driver) carefully. There is no glue between them: the only thing keeping them together is grit.
• There are two zebras, up and down of the screen. These zebras may be elastomeric or metallic. In both cases, clean them with a lint-free paper embedded in Caig Deoxit. You will be surprised at how black the paper comes, in case of the elastomeric connector! Do not use a cotton swab since it leaves fibers that will prevent a good connection. Repeat until paper comes clean. Also clean other grit you may see.
• Put both halves back together. There will be only one possible position if you align the holes properly.
• Put back the clips. To do that, first make sure that the two plastic "L" are aligned and slightly out on one side, to facilitate the entry. Second, take care that the two dents are on the circuit side, not the screen's. Then, starting from one side, slide the clip over the screen. It will not be scratched since the plastic L should protect it. Be careful again with bending or damaging the pins!. Once finished, do it with the other side. The plastic Ls are critical to maintain isolation and avoid damaging the screen.
• Solder back the screen. 

- One of the two screen driving circuits gone bad. This typically results on half of the 10 digits not working. This tends to happen when someone burns the circuit by inserting A24 batteries instead of N-type, subjecing the circuit to 96 volts instead of 6. The only solution is to find a donor machine and replace the screen. Use a small soldering gun and help lifting the pins with the tip of a plier, one by one. To solder the new one, follow the procedure in the above paragraph.